Molecular flexibility operated mesomorphism by end groups in azoester series

Abstract

ABSTRACTA novel azoester homologous series, RO‒C6H4‒COO‒C6H4‒N = N‒C6H4‒OC7H15(n) (para) has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on mesomorphic properties with reference to tthe flexible terminal chain. The novel azoester series consists of thirteen (C1–C18) members. Mesomorphism commences from C5 homologue. C1–C4 homologues are nonmesomorphic, C5 homologue is only nematogenic and C6–C18 homologues are smectogenic and nematogenic. All mesogenic homologues are enantiotropically mesomorphic. Transition temperatures and textures were determined by polarizing optical microscopy (POM) and a heating stage. Cr-M/I transition curve follows a zigzag path of rising and falling values and behaves in a normal manner. The Sm-N and N-I transition curves of a phase diagram behave in the normal established manner except for a small deviation for the higher homologues (C14 and C16). An odd-even effect is exhibited by Sm-N and N-I transition curves. Analytical spectral and thermal data support the molecular structures. Smectic and nematic thermal stabilities are 93.62°C and 114.3°C, respectively. Smectic and nematic mesophas elengths range from 12.0°C to 18.0°C and 11.0°C to 31.0°C. The series is predominantly nematogenic and partly smectogenic and of middle order melting type. Group efficiency order derived for smectic and nematic. Smectic and nematic: ‒OCH3 > ‒OC4H9 > ‒OC7H15(n).